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Mobile Communication: From 1G to 4G

Personal communication systemPersonal communication system (PCS) is a new class of cellular telephone system such as AMPS. PCS systems are a

combination of cellular telephone network and intelligent network, which is the entity of super-simple transfer (SST)

inter-office protocol tha distinguishes physical components of the switching network such as signal service point, signal

control point and signal transfer point from the services provided by SST network.

In essence, PCS is the North American implementation of European GSM standard. GSM utilised its own TDMA access

methods and provided expanded capacity and unique services such as caller ID, call forwarding and short messaging. A

critical feature was seamless roaming, which allowed subscribers to move across provider boundaries. The effort was

directed towards second-generation cellular systems.

In 1990, a second frequency band was specified. This band included twodomains—1710-1785 MHz and 1805-1880 MHz,

i.e., twice 75 MHz; three times as much as the primary 900MHz band.

Digital enhanced cordless telecommunication (DECT). DECT is a type of PCS system. DECT standard was developed

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by European Telecommunication Standards Institute (ETSI) for wireless PABX data LAN applications that represent

closed environments requiring minimal open cordless access, since it was essential that products from different vendors

not only coexist but interwork with each other.

DECT system has a TDMA/TDD frame structure with 24 slots that are equally allocated for downlink and uplink

operation. DECT specifiesboth simplex (half-slots) and duplex (full slot) operation. Higher data rates are achieved by

utilising multilevel modulation. The basic modulation scheme is a two-level Gaussian filled frequency-shif keying

(GFSK), which is supplemented with 8-level modulation scheme leading to as high as 2.88 Mbps per carrier.

GSMGlobal system for mobile communications (GSM) was developed by the Groupe Special Mobile, which was an initiative

of the Conference of European Post and Telecommunications (CEPT) administrations. GSM was firs devised as a cellular

system in a specific 900MHz band called the primary band. This primary band includes two sub-bands of 25 MHz each,

890-915 MHz and 935-960 Mhz.

GSM systems like Iridium, Globalstar and ICO use constellations of low-earth orbit (LEO) or medium-earth orbit (MEO)

satellites and operate as overlay networks for existing cellular and PCS networks. Using dual-mode, these extend the

coverage to any and all locations on the earth’s surface.

GPS—a reliable navigational aid anywhere onthe earth

International Mobile Telecommunication-2000 (IMT-2000) is a standard developed by ITU for 3G. It ensures global

mobility in terms of global seamless roaming and service delivery. An appreciation of the role of numbering and

identities in mobility management, international roaming, call delivery, and billing and charging is important inunderstanding the operation of mobile and personal communication networks.

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Personal communication satellite service (PCSS) uses LEO satellite repeaters incorporating QPSK modulation and both

FDMA and TDMA.

The main advantages of GSM are international roaming (in harmony with ISDN principles assuring inter-working

between ISDN and GSM) and features like privacy and encryption, frequency hopping, discontinuous transmission and

short message service. Other facilities include call forwarding, barring, waiting, hold and teleconferencing.

The basic architecture comprises a network sub-system, base station sub-system, mobile stations, and system

interworking and interfaces.

A subscriber identity module (SIM) is required to activate and operate a GSM terminal. The SIM may be contained within

the mobile station or it may be a removable unit that can be inserted by the user in his mobile set.

New developments along the way

Before we proceed to evolution from 1G to 4G, let me touch upon the new developments that took place in 1G to 4G.

Global positioning system (GPS). GPS is a reliable navigational aid available anywhere on the earth, operating in all

weather conditions 24 hours a day. It can be used by marine, airborne and land users. GPS technology was developed in

1983.

GPS consists of three segments:

Space segment. GPS consists of 24 NAVSTAR satellites along with three spare satellites orbiting at 20,200 km above

the earth’s surface in six circular orbital planes with a 12-hour orbital period each. These satellites operate at L1 band

(1.575 GHz) continuously broadcasting navigational signals called coarse acquisition code. These codes can be received

by anyone for decoding and findingnavigational parameters like longitude, latitude, velocity and time.

Control segment. It consists of a master control station (MCS) and a number of smaller earth stations called

monitoring stations located at different places in the world. Monitoring stations track satellites and pass on the

measured data to the MCS. The MCS computes satellite parameters (called ephemeris) and sends them back to the

satellite, which, in turn, broadcasts to all GPS receivers.

User segment. The user segment consists of all moving and stationary objects with GPS receivers. A GPS receiver is a

multi-channel satellite receiver that computes every second its own location and velocity.

Bluetooth. Compared to WLAN technologies, Bluetooth technology aims at so-called ad-hoc piconets, which are local-area networks with a very limited coverage and without the need for an infrastructure. The term ‘piconet’ is a collection

of Bluetooth devices that are synchronised to the same hopping sequence. One device in the piconet can act as master

and all other devices connected to the master act as slaves. The master determines the hopping pattern and the slaves

have to synchronise to this pattern. The hopping pattern is determined by the device ID—a 48-bit worldwide unique

identifier.The phase in the hopping pattern is determined by the master’s clock. All active devices are assigned a 3-bit

active member address.

All parked devices use an 8-bit parked member address. Devices in standby mode do not need an address. The goal for

Bluetooth development was to use a single-chip, low-cost, radio-based wireless network technology for laptops,

notebooks, headsets, etc.

Bluetooth operates in the 2.4GHz ISM band. However, MAC, physical layer and the offered services are completelydifferent. Bluetooth transceivers use Gaussian FSK for modulation and are available in three power classes: Class 1

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(max. power 100 mW), class 2 (max. power 2.5 mW) and class 3 (max. power 1 mW).

Journey from 1G to 4G

1G system. 1G specifications were released in 1990 to be used in GSM. 1G systems are analogue systems such as

AMPS that use FDM to divide the bandwidth into specificfrequencies that are assigned to individual calls.

2G system. These second-generation mobile systems are digital and use either TDMA or CDMA method. Digital cellular

systems use digital modulation and have several advantages over analogue systems, including better utilisation of

bandwidth, more privacy, and incorporation of error detection and correction.

2.5G system. It was introduced mainly to add latest bandwidth technology to the existing 2G generation. It supports

higher-data-rate transmission for Web browsing and also supports a new browsing format language called wireless

application protocol (WAP). The different upgrade paths include high-speed circuit-switched data (HSCSD), GPRS and

EDGE.

HSCSD increases the available application data rate to 14.4 kbps as compared to 9.6 kbps of GSM. By using four

consecutive time slots, HSCSD is able to provide a raw transmission rate of up to 57.6 kbps to individual users.

GPRS supports multi-user network sharing of individual radio channels and time slots. Thus GPRS supports many more

users than HSCSD but in a bursty manner. When all the eight time slots of a GSM radio channel are dedicated to GPRS,

an individual can achieve as much as 171.2 kbps. But this has not brought any new evolution.

EDGE introduces a new digital modulation format called 8-PSK (octal phase-shift keying). It allows nine different air

interface formats, known as multiple modulation and coding schemes, with varying degree of error control and

protection. These formats are automatically and rapidly selectable. Of course, the covering range is smaller in EDGE

than in HSCSD or GRPS.

3G system. To overcome the short-comings of 2G and 2.5G, 3G has been developed. It uses a wideband wireless

network that offers increased clarity in conversations. Countries throughout the world are currently determining new

radio spectrum bands to accommodate 3G networks. ITU has established 2500-2690MHz, 1700-1855MHz and 806-

960MHz bands. Here the target data rate is 2 Mbps. The data is sent through packet switching. Voice calls are

interpreted through circuit switching.

3G W-CDMA (UMTS). Universal Mobile Telecommunication System (UMTS) or W-CDMA assures backward compatibility

with 2G and 2.5G TDMA technologies . W-CDMA, which is an air interf ace standard, has been designed for always-onpacket-based wireless service, so that computers and entertainment devices may all share the same wireless network

and connect to the Internet anytime, anywhere.

W-CDMA supports data rates of up to 2.048 Mbps if the user is stationary, thereby allowing high-quality data,

multimedia, streaming audio, streaming video and broadcast type services to consumers. With W-CDMA, data rates

from as low as 8 kbps to as high as 2 Mbps can be carried simultaneously on a single W-CDMA 5MHz radio channel, with

each channel supporting between 100 and 350 simultaneous voice calls at once, depending on antenna sectoring,

propagation conditions, user velocity and antenna polarisation.

Time slots in W-CDMA are not used for user separation but to support periodic functions. (This is in contrast to GSM

where time slots are used to separate users). The bandwidth per W-CDMA channel is 4.4 to 5 MHz.

Since the global standard was diffiult to evolve, three operating modes have been specified:A 3G device will be a

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personal, mobile, multimedia communication device (e.g., TV provider redirects a TV channel directly to the subscriber’s

phone where it can be watched). Second, it will support video conferencing, i.e., subscribers can see as well as talk to

each other. Third, it will also support location-based services, where a service provider sends localised weather or

trafficconditions to the phone or the phone allows the subscriber to findnearby businesses or friends.

3.5G. It supports a higher through-put and speed at packet data rates of 14.4 Mbps, supporting higher data needs of

consumers.

4G system. It offers additional features such as IP telephony, ultrabroadband Internet access, gaming services and

HDTV streamed multimedia. Flash-OFDM, the 802.16e mobile version of WiMax (also known as WiBro in South Korea),can support cellular peak data rates of approx. 100 Mbps for high-mobility communications such as mobile access and

up to 1 Gbps for low-mobility communications such as nomadic/local wireless access, using scalable bandwidths of up to

40 MHz. The infrastructure for 4G is only packet-based (all-IP).

The author is director (R&D) at Global Institute of Technology, EPIP Sitapura, Jaipur

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